1. Field of the Invention
The invention relates to a valve control for a gas exchange valve in an internal combustion engine, with at least one spring element preloading the valve in at least one end position, and a fixing device for the releasable fixing of the valve.
2. Description of the Related Art
A multiplicity of valve controls for gas exchange valves in internal combustion engines are known from the prior art. Generally, mechanical, hydraulic or electrical valve controls can be distinguished.
With purely mechanical valve controls the actuation of the gas exchange valve is controlled through a cam whose actuation is transmitted through suitable mechanical transmission elements such as pushrods, rocker arms and similar. The disadvantage of these purely mechanical valve controls is that the actuation of the gas exchange valve is directly coupled to the operation of the engine and adjusting of the opening time or even the actuation travel of the gas exchange valve is at best possible with major technical expenditure.
In the case of purely hydraulic and electrical valve controls the actuation of the gas exchange valve is performed with the help of hydraulic or electrical actuation devices which directly or indirectly act on the gas exchange valve. In the process, opening times, opening speeds and actuation travels of the gas exchange valve can be specifically set by corresponding activation of the actuation devices and, as a function of the operating parameters of the internal combustion engine such as the rotational speed, the rotational moment, the emission values or the operating temperature of the internal combustion engine can be modified.
An example for a hydraulic valve control is shown by U.S. Pat. No. 4,930,464, wherein the gas exchange valve is guided in an hydraulic actuation chamber with the help of a piston section and mechanically clamped through two compression springs opposing each other. The piston section subdivides the actuation chamber into two chamber sections which are in connection with a hydraulic supply so that the piston section is hydraulically clamped in. For adjusting the gas exchange valve the two chamber sections are each specifically filled with a hydraulic fluid or said fluid drained from one or the two chamber sections, wherein the actuation movement is supported by the two compression springs.
U.S. Pat. No. 5,673,658 shows a hydraulic valve control wherein the stem of the gas exchange valve is mechanically clamped in through two compression springs opposing each other, wherein in the rest position the compression spring near the valve disc preloads the gas exchange valve in its closed end position. For adjusting the gas exchange valve a hydraulic actuation device is provided at its end facing away from the valve disc with which, through support of the other compression spring far from the valve disc the gas exchange valve can be opened against the force of the compression spring close to the valve disc. In addition, a fixing device likewise to be actuated hydraulically is provided with which the gas exchange valve can be releasably fixed or secured in its closed end position, an intermediate position and a completely open position.
The disadvantage of this hydraulic valve control known from U.S. Pat. No. 5,673,658 is that although the valve control has improved adjustability and variability of the opening times, the opening durations and the actuation travels of the gas exchange valves compared with purely mechanical valve controls, comparatively high hydraulic forces have to be generated because of the spring arrangements in order to actuate the gas exchange valve.